Reviewed by Dirk Schulze.

        Save additional memory in SVG*Element classes, by introducing SVGElementRareData
        https://bugs.webkit.org/show_bug.cgi?id=34268

        Introduce SVGElementRareData, to remove the need to store any members in SVGElement/SVGStyledElement.
        This saves some additional MB for the svg-node-count-vs-scroll.xhtml testcase.

        SVGElementRareData works just like NodeRareData. Unlike ElementRareData, we're not inheriting from
        NodeRareData in SVG, as we don't need all the rare data stored there, unlike Element.

        * GNUmakefile.am: Add SVGElementRareData.h to build.
        * WebCore.gypi: Ditto.
        * WebCore.pro: Ditto.
        * WebCore.vcproj/WebCore.vcproj: Ditto.
        * WebCore.xcodeproj/project.pbxproj: Ditto.
        * dom/Node.cpp: Use Nodes bitfield to keep track wheter a SVGElement has a SVGElementRareData object associated.
        (WebCore::Node::Node):
        * dom/Node.h: Add m_hasRareSVGData flag, merged with the existing bitfield, 10 bits remaining now.
        (WebCore::Node::hasRareSVGData):
        * svg/SVGAnimateMotionElement.cpp: SVGElement::instancesForElement() now returns a const-reference to the HashMap instead of copying.
        (WebCore::SVGAnimateMotionElement::applyResultsToTarget):
        * svg/SVGAnimateTransformElement.cpp: Ditto.
        (WebCore::SVGAnimateTransformElement::applyResultsToTarget):
        * svg/SVGAnimationElement.cpp: Ditto.
        (WebCore::SVGAnimationElement::setTargetAttributeAnimatedValue):
        * svg/SVGElement.cpp: Move the element instances HashSet and two cursor-related pointers into SVGElementRareData.
        (WebCore::SVGElement::SVGElement):
        (WebCore::SVGElement::~SVGElement):
        (WebCore::SVGElement::rareSVGData): Modelled just like Node::rareData().
        (WebCore::SVGElement::ensureRareSVGData): Dito.
        (WebCore::SVGElement::accessDocumentSVGExtensions):
        (WebCore::SVGElement::mapInstanceToElement): Route call through SVGElementRareData.
        (WebCore::SVGElement::removeInstanceMapping): Ditto.
        (WebCore::SVGElement::instancesForElement): Ditto.
        (WebCore::SVGElement::setCursorElement): Ditto.
        (WebCore::SVGElement::setCursorImageValue): Ditto.
        * svg/SVGElement.h:
        * svg/SVGElementInstance.cpp: Ditto.
        (WebCore::SVGElementInstance::invalidateAllInstancesOfElement):
        * svg/SVGElementRareData.h: Added. Based on NodeRareData - works exactly the same.
        (WebCore::SVGElementRareData::SVGElementRareData):
        (WebCore::SVGElementRareData::rareDataMap):
        (WebCore::SVGElementRareData::rareDataFromMap):
        (WebCore::SVGElementRareData::elementInstances):
        (WebCore::SVGElementRareData::instanceUpdatesBlocked):
        (WebCore::SVGElementRareData::setInstanceUpdatesBlocked):
        (WebCore::SVGElementRareData::cursorElement):
        (WebCore::SVGElementRareData::setCursorElement):
        (WebCore::SVGElementRareData::cursorImageValue):
        (WebCore::SVGElementRareData::setCursorImageValue):
        * svg/SVGStyledElement.cpp: Move m_instancesUpdatesBlocked into SVGElementRareData.
        (WebCore::SVGStyledElement::SVGStyledElement):
        (WebCore::SVGStyledElement::instanceUpdatesBlocked):
        (WebCore::SVGStyledElement::setInstanceUpdatesBlocked):
        * svg/SVGStyledElement.h:
        * svg/SVGUseElement.cpp: Adapt to element instances changes, now passed as const-reference.
        (WebCore::dumpInstanceTree):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@54009 268f45cc-cd09-0410-ab3c-d52691b4dbfc